Half of the illegal emissions of a chlorofluorocarbon (CFC) gas have been identified as coming from just two Chinese provinces. Although partially anticipated, the findings will assist moves to track down the source before they destroy the Earth's protective ozone layer.
The discovery in the 1980s that certain gases, principally CFCs, were destroying the stratospheric ozone in polar regions led to perhaps the world's most successful environmental treaty. The Montreal Protocol caused the rapid phase-out of the most dangerous gases and slower reductions in the use of other contributors. As a result, the ozone layer, which shields the Earth from lethal ultraviolet radiation, has started to heal.
With the entirety of life on Earth at stake, scientists have been wary of complacency and are monitoring atmospheric concentrations of the now-banned gases, particularly CFC-11 and CFC-12. Last year, alarms sounded when the rate of decline of CFC-11 concentrations was found to be slowing sharply, indicating new gas was replacing some of what was breaking down.
A new paper in Nature uses observations from Korea and Japan to show that 7,000 tonnes more CFC-11 a year was released from eastern China in 2014-2017 than during 2008-2012. This accounts for 40-60 percent of the global anomaly. Under the protocol, CFC-11 use was banned from 2010, with alternatives becoming so widely available its use was entirely unnecessary.
Worldwide, some CFC-11 is still released from slowly leaking building foams installed before the ban. This source is small enough to do only modest damage and is expected to decline with time. The increase in recent years indicates new production, which if not brought under control could be far more serious.
From the start, China was thought to be the most likely source of these emissions. Within weeks, New York Times journalists identified eight factories using the banned chemical as a refrigerant, with some claiming not to know it was illegal. Important as that investigation was, it couldn't measure if those factories were the whole problem or if there were other issues elsewhere.
Dr Sunyoung Park of Kyungpook National University, Korea, turned to gas chromatography of atmospheric samples taken many times a day in Gosan, South Korea, and Hateruma, Japan, to explore the question from a different angle. CFC-11 levels are still declining globally, but this has slowed sharply at Hateruma and ceased entirely at Gosan. The source had to be nearby. Using wind patterns and a comparison of concentrations at different sites, Park identified Shandong and Hebei as the main CFC-11 sources.
The origins of the rest of the CFC-11 being added to the atmosphere remains a mystery. “We find no evidence for a significant increase in CFC-11 emissions from any other eastern Asian countries,” Park and co-authors write. Facilities on other continents found no evidence of increasing sources nearby.